1. Field of Invention
This invention relates to systems and apparatus for recycling scavenged power from a pin scorotron grid to drive a discorotron grid in an electrophotographic or xerographic system.
2. Description of Related Art
The xerographic imaging process is initiated by charging a charge retentive surface, such as that of a photoconductive member, to a uniform potential. The charge retentive surface is then exposed to a light image of an original document, either directly or via a digital image driven laser. Exposing the charged photoconductor to light selectively discharges areas of the charge retentive surface while allowing other areas to remain unchanged. This creates an electrostatic latent image of the document on the surface of the photoconductive member.
Developer material is then brought into contact with the surface of the photoconductor material to develop the latent image into a visible reproduction. The developer typically includes toner particles with an electrical polarity that is the same as, or that is opposite to, the polarity of the charges remaining on the photoconductive member. The polarity depends on the image profile.
A blank image receiving medium is then brought into contact with the photoreceptor and the toner particles are transferred to the image receiving medium. The toner particles forming the image on the image receiving medium are subsequently heated, thereby permanently fixing the reproduced image to the image receiving medium.
Electrophotographic or xerographic laser printers, scanners, facsimile machines and similar document reproduction devices must be able to maintain proper control over the systems of the image forming apparatus to assure high quality output images. For example, the level of electrostatic charge on the photographic member must be maintained at a certain level to be able to attract the charged toner particles.
FIG. 1 shows an exemplary embodiment of an image forming apparatus 100 having a photoreceptor 120. The image forming apparatus 100 can be a xerographic printer or other known or later developed xerographic device. It should be appreciated that the specific structures of the image forming apparatus are not relevant to this invention and thus are not intended to limit the scope of this invention.
As shown in FIG. 1, one or more latent images can be generated on the photoreceptor 120 in any well known manner, by controlling one or more of a number of different developer units 150A, 150B, 150C and 150D using controller 110.
In many xerographic machines, where high image quality targets are desired, the photoreceptor is first charged using a pin scorotron device, and then recharged, or charge leveled, by a discorotron device. For example, as shown in FIG. 1, in the direction of movement of the photoreceptor 120, as indicated by the arrows, to lay a first level of toner onto the photoreceptor, the photoreceptor 120 is charged by charge/recharge device 130E having a pin scorotron and a discorotron device. Next, the charge laid by the charging device is exposed by exposing unit 140E and finally, the toner is developed by developing unit 150E. The process continues in the direction of movement of the photoreceptor until all layers of toner are laid to complete an image-on-image full-color image forming process. Once the full-color image is finished, the completed image is transferred to a sheet of image recording media 160.
The charging procedure of the charge/recharge device is performed to produce a very uniform charge on the photoreceptor. This uniform charge is especially important in the image-on-image type xerographic color machines, as shown in FIG. 1, where the photoreceptor may be buried under multiple layers of toner. Typically, the pin scorotron device is set to charge the photoreceptor to a voltage slightly higher than the final voltage, and the discorotron is then used to discharge the photoreceptor uniformly to the desired voltage.
FIG. 2 represents a typical configuration of a charge/recharge system 200 that is usable in a xerographic system. The left side of the configuration represents the pin scorotron device 270, while the right side of the configuration represents the discorotron device 210. In the pin scorotron device 270, a high-voltage DC signal is applied to the pins 240 by a pin current supply 250. The applied voltage is sufficiently high to cause corona discharge at the pins 240. This discharge provides a path for a pin current to be applied to a pin scorotron grid 245. The pin scorotron grid 245 is located between the photoreceptor 120 and the pins 240 so that the majority of the pin current is absorbed by the pin scorotron grid 245. The grid is held at a constant voltage by the pin scorotron grid voltage control circuit 260, which is a simple shunt regulator type circuit. The pin scorotron grid voltage control circuit 260 operates in a linear manner to achieve a variable resistance network to ground. The resistance of the pin scorotron grid voltage control circuit 260 can be controlled to either increase or decrease its voltage drop to achieve the desired grid voltage.
The discorotron device comprises a shield 225 formed of aluminum or the like and having an open lower end, a corona discharge electrode 230, such as a glass coated tungsten wire or the like, extending within the shield 225, and a discorotron grid 235 disposed opposite the opening of the shield 235 and between the shield 225 and the photoreceptor 120. The discorotron device 210 operates in much the same manner as the pin scorotron device 270. The discorotron grid 235 is typically driven by an active power source, such as the grid voltage active control circuit 215. The discorotron high-voltage AC source 220 is connected to the corona discharge electrode 230 to produce a corona discharge.
As shown in FIG. 2, the pin scorotron device 270 and the discorotron device 210 are driven by separate power supplies. However, there is available power in the pin scorotron grid voltage control circuit 260 that can be recycled and used to drive and control the discorotron grid 235.
The inventors have discerned that the power that is dissipated in the pin scorotron grid voltage control circuit 260 can be used to drive the discorotron grid 235.
This invention provides systems and apparatus that provide reduced power dissipation in the high voltage power supply.
This invention separately provides possible direct programming of the voltage applied to the photoreceptor and the voltage between the pin scorotron grid and the discorotron grid rather than by indirect programming of the voltage applied directly to the pin scorotron grid and the discorotron grid.
This invention separately provides reduced electromagnetic emissions and increased arc immunity of the discorotron due to a better controlled xerographic current path. The reduced emissions is achieved because the discorotron grid is not driven by an active power supply.
In various exemplary embodiments of the systems and apparatus of this invention, the active power source that is typically used to drive the discorotron grid is removed. According to the systems and apparatus of this invention, the discorotron grid instead utilizes a combined circuit which uses the power dissipated in the traditional shunt regulation circuit that drives the pin scorotron grid to drive the discorotron grid through a series pass regulation circuit. The current flow of the combined circuit naturally flows in a direction to allow shunt regulation of the pin scorotron grid while also providing an active drive voltage for the discorotron grid.
These and other features and advantages of this invention are described in or are apparent from the following detailed description of the apparatus and systems according to this invention.